RESUMO
Objective To investigate the effect of PKC? antisense oligonucleotides injected intrathecally on the hyperalgesia and expression of PKC? protein in rats with chronic morphine tolerance. Methods Twenty-four female SD rats weighing 150-180 g were randomly divided into 4 groups ( n = 6 each): group Ⅰ control; group Ⅱ morphine (M); group Ⅲ sense oligonucleotides (S) and group Ⅳ antisense oligonucleotide (A) . An intrathecal catheter was placed in the lumbar subarachnoid space to allow for bolus injections. Chronic morphine tolerance was induced by intrathecal morphine 20 ?g twice a day (at 8:00 and 16:00) for 5 consecutive days. Intrathecal morphine (20 ?g twice a day) was continued in group M, S, and A and normal saline 20 ?l (in group M) or sense oligonucleotide 20 ?g (in group S) or antisense oligonucleotide 20 ?g (in group A) was given intrathecally between the two morphine doses (at 12: 00) for 6 consecutive days. Pain threshold was assessed by measuring the withdrawal response of the hindpaw to radiant heat with a thermal plantar testing apparatus 2 days before intrathecal catheter was placed and on the 2nd, 4th and 6th day after morphine tolerance was induced. The animals were killed on the 6th day of intrathecal NS/oligonucleotide administration after pain threshold was measured. The L2-6 segment of spinal cord was removed for determination of the expression of PKC? mRNA (RT-PCR) and PKC? protein (Western blot) .Results The establishment of morphine tolerance was confirmed by significant shortening of response latency to radiant heat. The thermal withdrawal latency was significantly prolonged in group S and A after intrathecal administration of sense or antisense oligonucleotide as compared with group M but was significantly shorter in group S than in group A. The expression of PKC? protein in spinal dorsal horn was significantly decreased in group S and A as compared to group M, but was significant lower in group A than in group S. The PKC? mRNA expression was significantly lower in group A than in group M but there was no difference in PKC? mRNA expression between group S and M. Conclusion The hyperalgesia induced by chronic morphine tolerance can be reversed by intrathecal PKC? antisense oligonucleotide through reduction of PKC? protein expression in the spinal dorsal horn.
